The present invention concerns digital signal transformation, such as digital filtering.
Many digital filtering methods and devices are known. By way of example, analysis filterings and corresponding synthesis filterings of digital signals are envisaged here. Combined analysis and synthesis filterings are also envisaged.
These filterings are generally sub-assemblies integrated into the coding and/or decoding assemblies. They often require a large random access memory or buffer memory space, for storing the data being processed.
The present invention provides a digital signal transformation method and device which minimises the buffer memory occupancy of the data being processed.
To this end, the invention proposes a digital signal transformation method, original samples of the digital signal being transformed into output samples, any output sample being calculated by a function of original samples, and/or of intermediate samples, and/or of output samples.
characterised in that:
each function is broken down into elementary operations;
the elementary operations of all the functions are ordered so that the number of samples necessary simultaneously is a minimum.
By virtue of the invention, the buffer memory occupancy of the data being processed is reduced compared with the prior art. Thus, powerful filterings can be integrated into many appliances, without these requiring very large memories.
According to preferred and alternative characteristics:
the transformation is a filtering for analysis of the digital signal into interlaced frequency sub-band signals,
the transformation is a filtering for synthesis of a digital signal analyzed into interlaced frequency sub-band signals, into a synthesized signal or
the transformation is a filtering for analysis of a digital signal into interlaced frequency sub-band signals, combined with a filtering for synthesis of the signal analyzed into interlaced frequency sub-band signals, into a synthesized signal.
These transformations are frequently used in coding and decoding methods and devices, and for this reason it is of interest to improve their implementation by virtue of the present invention.
According to a preferred characteristic, the elementary operations are functions of samples, at least one multiplying factor of which is equal to one. The calculations require fewer multiplications and are thus simplified.
According to another preferred characteristic, the output samples are multiplied by a normalization factor.
According to preferred characteristics, the digital signal is an image signal and the original samples are lines or columns of the image. The invention applies advantageously to an image signal, which generally requires a large memory space. This memory space is reduced by virtue of the invention.
Correlatively, the invention proposes a digital signal transformation device, original samples of the digital signal being transformed into output samples, the device having means for calculating any output sample by a function of original samples, and/or of intermediate samples, and/or of output samples,
characterised in that the calculation means are adapted to:
break down each function into elementary operations;
order the elementary operations of all the functions so that the number of samples necessary simultaneously is a minimum.
The device has means of implementing the characteristics explained previously.
The invention also concerns a digital apparatus including the transformation device or means of implementing the transformation method. This digital apparatus is for example a digital camera, a computer, a facsimile machine, a photocopier, a scanner or a printer.
The advantages of the device and the digital apparatus are identical to those explained previously.
A means of storing information, readable by a computer or a microprocessor, integrated or otherwise with the device, possibly removable, stores a program implementing the filtering method.